Prove that the degree of polarization $\left(V_{r}\right)$ of reflected light can be expressed as $$V_{r}=\frac{R_{\perp}-R_{\|}}{R_{\perp}+R_{\|}}$$
[Hint: For unpolarized reflected light $I_{r_{1}}=I_{r \perp},$ whereas for polarized reflected light $\left.I_{p}=I_{r \perp}-I_{r \|-}\right]$